1. Field of the Invention
This Invention relates to the field of Gas Turbine Engines, and, generally to airfoils and, more particularly, to ceramic turbine airfoils with a metal internal support structure.
2. Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98
Gas Turbine Engines include a turbine with a plurality of rows of rotating blades and stationary vanes, or airfoils. Airfoils are generally made hollow, with air cooling passages therein to provide cooling for the airfoil. The external surfaces of the airfoil are subjected to high temperatures from the flowing gas. Cooling a turbine airfoil prolongs the turbine airfoil useful life and improves turbine airfoil performance.
A hollow airfoil may have a metal insert secured within the airfoil by a resin matrix, possibly including a fibrous material embedded within the matrix. One problem with the prior art is that the metal material of the insert does not bond well to the resin matrix. With a weak bond, the insert can slide out of the hollow airfoil under light loads.
FIG. 1 show a helicopter blade 20 secured to a rotor of a driving engine. The rotor includes a blade mounting portion 10 having an annular recess 12 formed completely around the shaft of the blade mounting portion. The blade includes fingers 22 extending inward and toward the annular recess of the mounting portion 10. Each finger 22 includes a hoop fiber arrangement 30 extending in an annular arrangement around the fingers 22. The hoop fibers 30 form a bump portion extending inward from the fingers 22 and align with the annular recess 12 formed in the blade-mounting portion 10. The hoop fibers 30 are formed within a resin matrix, forming a fibrous composite material. Because of the strength of the fibers within the matrix, the blade is securely attached to the rotor mount even under the extremely high centrifugal forces developed during high-speed rotation of the blades about the rotor. In order for the blade to slip out of the blade mount, the fibers would have to break.
FIG. 2 shows an airfoil known in the prior art and shown in U.S. Pat. No. 4,249,291. A plurality of holes 24 are drilled in an oversized airfoil core blank 25 at spaced locations corresponding to the desired locations of cooling tubes in the airfoil. The cooling tubes are separately fabricated as preassembled composite tube inner member 27 within an outer member 26 and are inserted into the holes 24 formed in the airfoil blank 25. The so-inserted composite tubes 27 are then HIP diffusion bonded or brazed in place.
U.S. Pat. No. 4,563,128 issued to Rossmann on Jan. 7, 1986 shows a Ceramic turbine Blade Having A Metal Support Core in which a hollow ceramic blade member is supported between flanges on a metal core, or by a core head attached at an end of a metal rod passing though a hollow portion of the ceramic blade.
U.S. Pat. No. 4,790,721 issued to Morris et al on Dec. 13, 1988 shows a Blade Assembly in which a ceramic blade jacket is supported on a metallic core between a lower flange extending from a root of the blade and a top flange formed on the metallic core.
U.S. Pat. No. 4,314,794 issued to Holden, deceased et al on Feb. 9, 1982 shows a plurality of hollow ceramic washers in the shape of a blade supported on a metal core, a bolt securing the metal core to a ceramic root portion of the blade.
U.S. Pat. No. 4,285,634 issued to Rossmann et al on Aug. 25, 1981 shows a gas turbine blade constituted of a supportive metallic blade core and a thin-walled ceramic blade airfoil, in which the airfoil is supported against a tip plate of the blade core. The blade core consists of rod or wire-shaped pins which have widened bases at their radially inner ends. Through these widened bases, the pins are retained in a metallic adapter slidably into a turbine disc.
U.S. Pat. No. 2,479,057 issued to Bodger on Aug. 16, 1949 shows a ceramic blade secured to a metallic post by a shroud segment welded to the metallic post, the shroud segment forming a flange to hold the ceramic blade onto the metallic post.
U.S. Pat. No. 6,514,046 issued to Morrison et al on Feb. 4, 2003 shows a vane assembly for a turbine assembly includes an inner end cap, an outer end cap, and a body. The body includes a metallic core assembly, a ceramic shell assembly and a support assembly. The metallic core assembly is coupled to the inner and outer end caps and bears most of the mechanical loads, including aerodynamic loads. The ceramic shell bears substantially all of the thermal stress placed on the vane assembly. The support assembly is disposed between the metallic core assembly and said ceramic shell assembly and is coupled to the metallic core assembly.
The above cited prior art references do not have strong bond between a metallic insert and a blade or vane body made of a ceramic material that can withstand modern high stresses in the airfoil that tend to separate the metallic material from the ceramic material.
It is therefore an object of the present invention to provide a high strength bond between a metallic insert and an outer ceramic airfoil member, the airfoil being a blade or vane used in a gas turbine engine.